It is often desirable to provide wireless communication rather than wired communication using cables between related pairs of devices separated by a short distance. Devices that communicate using cables often require the devices to be located in close proximity to each other as dictated in part by the length of the cables. In contrast, wireless communication decreases the amount of cabling between electronic devices and thus increases the ease of use and convenience for the user. Further the wireless communication devices, such as a portable electronic device, may add more security and may be more aesthetic. With wireless communication, the distance between the related devices is generally only limited by the limits of the wireless signal transmission and reception systems. Examples of related pairs of devices include a cordless headsets on the one hand and a telephone, computer, Personal Digital Assistant (PDA), television set, VCR, DVD player, video game player, stereo receiver, CD player, and MP3 player on the other hand. Other examples of related pairs of devices include a computer and its various external devices such as a monitor, printer, keyboard, mouse, telephone and speakers for example.
The portable electronic device comprises a small inbuilt antenna of high performance to perform as required. The antenna enables wireless communication between a radio unit in the portable electronic device and a radio unit in a corresponding unit. In general it is desirable to minimize the size of the portable electronic device so as to provide a device that is as discrete and as practical as possible. Thus the space for the antenna in the portable communication device is reduced almost day by day, resulting in a keen need of improvement for the antenna miniaturization.
The volume within the portable electronic device is governed by industrial design and may place restrictions on both the size of the antenna and the size of the ground plane. However the dimensions of the antenna residing within the portable electronic device are dictated by the wavelengths of the signals that the antenna is to receive and transmit as well as the form of the antenna. Examples of such signal wavelengths are e.g. Bluetooth 2400-2483.5 MHz which corresponds to a wavelength of about 12 cm in free space. Thus the antenna and the portable electronic device are designed with mutual consideration in order to accommodate the antenna within the portable electronic device.
Many types of antenna technologies may be chosen for the internal antenna of the portable electronic device. The selection depends upon the size and shape of the portable communication device volume into which the antenna must fit and the system performance requirements of the antenna.
A commonly known antenna is the T-antenna. The T-antenna comprises two wires, a first vertical or sloping wire and a second straight horizontal wire. The vertical wire is connected to the approximate central of the straight horizontal wire, thus forming the characteristic “T”-shape. The radiation pattern of a T-antenna is Omni-directional, just like a dipole antenna. The T-antenna is easily scalable relative to the used frequency(s). A disadvantage of a stretched-wire ½ wave dipole or T-antenna is the overall physical length of it. This makes it difficult to integrate it into a small product.
Meandered mono pole antennas are also commonly used in portable communication devices. The meandering pattern of the antenna enables a reduction of the overall physical length of the antenna element whilst retaining the same electrical length. Thus the meandered mono pole antenna is more scalable than the stretched wire dipole. The total length of a meandered monopole antenna is preferably chosen to be one quarter of the wavelength of the desired resonant frequency. However, other lengths could also be used for the resonator elements including three quarters, one and one quarter, ⅕'th etc. A disadvantage of a meandered monopole is still the relative large area it needs. The meandering of the antenna employs a relatively larger area compared to the area employed by a straight wire. Further the space between the meandering lines is unused. If this space is compromised to a minimum the bandwidth of the antenna is also compromised. This largely depends on the gab between the meandering pattern and the number of meanderings.
An Inverted F Antenna (IFA) is a planar antenna, having a low profile or a flat structure, that are commonly employed as internal antennas configured inside portable communication devices, such as handsets, operating in e.g. the 1900 MHz radio frequency band. A conventional Planar Inverted F Antenna (PIFA) includes a radiating element, a wire and a ground plane. The planar inverted F antenna is shaped like the letter F. The planar inverted F antenna, as well as, an inverted F antenna, both requires a relatively large ground plane to work correctly. This significantly limits the scalability of the F antenna types. Further the F antennas suffer from a narrow bandwidth characteristic which is a considerable limitation.
/Thus what is needed is an antenna for use in a portable communication device that meets the required communication performance without or with minimized performance degradation. Further it is highly desirable that the antenna is small, space efficient and light thus avoiding clumsy and unwieldy devices. In the case of the portable communication device being represented by a cordless headset it is further desirable that the antenna has a high efficiency when the headset is put in talk position, i.e. is arranged close to the body of the user.
The antenna should preferable also be configured to allow better placement of control switches, electronic components and/or buttons of the portable communication device. Ideally the antenna is also cost-effective to manufacture and easy to assemble.